The preparation of pipe ends for welding is frequently carried out by the use of portable lathes that cooperate with various mandrel devices, whereby the pipe is secured in a fixed position relative to the portable lathe by means of the mandrel and the lathe is then advanced along the mandrel assembly to perform a turning operation on the pipe end.
Exemplary of such pipe end preparation systems are those illustrated in U.S. Pat. Nos. 3,164,062, 3,229,555, 3,982,451, and 3,992,123. In accordance with the systems of the prior art, it will be readily observed that, in general, the pipe workpiece is engaged by an internal mandrel that radially expands to engage the internal diameter of the pipe. The mandrel is usually provided with an axially extending shaft that supports the portable lathe adjacent the end of the pipe. The lathe is provided with cutting tool bits that are orbitally driven by a power source or manually about the longitudinal axis of the lathe.
The portable lathe itself, in accordance with the prior art, is typically provided with a feed means that enables the lathe assembly to be advanced along the shaft of the mandrel to cause engagement of the cutting tool bits with the end of the pipe to be prepared for welding. Thus, after the mandrel is secured within the pipe, the tool head of the portable lathe is caused to rotate and the cutting bits are advanced into the pipe end to complete the preparation operation.
According to conventional prior art practice, the mandrel arrangements are conventionally designed to provide an accurate centering of the lathe along the longitudinal centerline of the pipe, and to position the cutting plane of the lathe perpendicular to the pipe axis, since it is somewhat critical in accordance with usual practice to turn a precise concentric and perpendicular surface on the end of the pipe in preparation for a subsequent welding operation. Thus, it will be seen from the prior art examples that conventional mandrels are arranged to rigidly support the portable lathe along the centerline of the pipe, and no provision whatsoever is made to permit any relative angular motion between the centerline of the lathe and the centerline of the mandrel after the mandrel is locked into position in the pipe.
This rigid interconnection between mandrel and lathe in accordance with the prior art functions in a desirable manner as long as the end of the pipe is to be machined in a cutting plane that is normal to the centerline of the pipe. However, in actual practice, it is often desirable to make a miter cut on the end of the pipe to enable the pipe to be welded to an adjacent pipe segment that is not in line with the first pipe.
Accordingly, the present invention was created to enable miter cuts to be made on the end of a pipe by a portable lathe to prepare the pipe for welding to another pipe section the centerline of which extends at an angle to the centerline of the first pipe.